Various type of collapsible ladders are known. One commonly known type known as a rope ladder comprises a pair of ropes that are attached to a series of rungs. U.S. Pat. No. 4,260,039 discloses a collapsible ladder that comprises a plurality of rungs and side support members comprising two generally rigid sections pivotally connected together. While such a ladder is more rigid than a rope ladder, the rigidity is less than desirable, particulary when used over regions lacking the support of a wall, such as at windows.
U.S. Pat. No. 4,231,449 discloses a foldable ladder that purports to provide rigidity. However, the construction is relative complex and appears to be expensive to manufacture.
The known collapsible ladders are not provided with means for controlling the rate of deployment which becomes a problem as the length and mass of the ladder increases.